1. Field of the Invention
The present invention relates to electrical generators, particularly, to size, weight, and reliability improvements of portable electric generators. A flywheel starter/alternator mounted on an air-cooled or water-cooled internal combustion engine generates electrical power when the engine is operating and can also be used to provide engine rotation for starting. The electrical configuration provides improved power surge capability and load leveling capability. Improvements in the engine design and the functionality of the integrated flywheel-alternator-starter result in a smaller and lighter generator with fewer components that is easier to transport, more reliable, and may be started in colder ambient conditions.
2. Description of the Related Art
Portable electric generators of the prior art are typically comprised of an air-cooled internal combustion engine coupled mechanically through a power takeoff shaft to an alternator. The power takeoff shaft is typically integral to the crankshaft on the side of the engine opposed to the engine flywheel, although power takeoff shafts integral to the camshaft on the side of the engine opposed to the engine flywheel are also common. The flywheel provides an inertial means of reducing shaft speed fluctuations that are created by the cyclic torque of reciprocating machines. In this configuration the alternator has its own set of bearings for supporting the alternator rotor, which is coupled to the power takeoff shaft through a flexible or rigid coupling. The alternator assembly is mounted on a frame common with the engine. To provide electric starting, an electric starter motor is typically mounted to the external surface of the engine and temporarily engages with the flywheel during the starting.
Typically, the end of the electric starter motor connects to a retractable pinion gear, such as a Bendix gear, which engages teeth on the engine flywheel, during motor starting, cranking the engine. Once the combustions cycle is self-sustaining, this pinion gear retracts, disengaging the Bendix gear from the teeth on the flywheel. Variations of engaging a starter motor to the engine for starting are also possible and well known in the art. Using a separate alternator coupled to the engine via the protruding crankshaft and a dedicated starter motor mounted on the engine and temporarily coupled to the engine through gear teeth (ring gear) on the flywheel is typically bulky and heavy due to lack of weight optimization and integration. Furthermore, alternator coupling failures due to misalignment and failure of the starter motor to engage or disengage, as well as gear wear can reduce the reliability of this type of system. Examples of such prior art generators include 2-kW Military Tactical Generator Sets (MTGs) by Dewey Electronics Corporation and Mechron Power Systems, Inc. The 2-kW, 120-VAC, 60-Hz Dewey MTG (model No. MEP 531A) has a dry weight of 143.1 lbs. and is comprised of a commercial alternator mounted to a Yanmar L48AE-DEG engine. The Yanmar engine has an externally mounted starter motor with a solenoid-actuated pinion gear to engage the ring gear mounted on the flywheel. The 2-kW, 28-VDC Dewey MTG (model No. MEP501A) has a dry weight of 123.5 lbs. and is comprised of a Balmar alternator mounted to the same Yanmar L48AE-DEG engine. The AC and DC versions of the Mechron 2-kW MTGs are also comprised of a commercial alternator mounted to the Yanmar L48AE-DEG engine and have dry weights of 141 lbs. and 126 lbs., respectively. In another common configuration, the alternator rotor is mounted directly on the power takeoff shaft and the alternator stator is fixed to the engine housing or engine block. The independent alternator shaft, bearings, bearing housing, and coupling of the first configuration are eliminated. This type of generator is typically assembled from a commercially available engine and an alternator designed specifically for the engine power takeoff shaft. While this configuration provides a size and weight improvement over the first configuration, full optimization and complete integration is still lacking. A separate externally mounted starter motor with an engage-able/dis-engage-able pinion gear rotating a ring gear on the flywheel is also still used. An example of such prior art includes Polar Power Inc. alternator model 3500 or 6250 mounted to commercial generators such as Yanmar's L40, L48, L70, or Lister Potter LPA2 engines. The dry weight of a Polar 35000 alternator mounted on a Yanmar L48AE-DE engine is 91 lbs. (not including instrumentation and generator frame).
Additional size and weight reductions can be achieved when the engine manufacturer is the same as the alternator manufacturer, or the manufacturer of the engine and the manufacturer of the alternator work in unison during the design phase to produce a system. Designing the engine and alternator simultaneously results in an optimized system, not just a system consisting of individually optimized components. The largest components of an electric generator are typically the engine block, the alternator, and the starter motor assembly. Therefore, the present invention is aimed at reducing the size and weight of these components through integration of the components and their functions.
Throughout the twentieth century, the majority of engine blocks were manufactured from cast iron. Lightweight alloys, primarily aluminum, replaced cast iron in mobile applications (automotive engines, marine engines, generator set engines, etc.). In the 1990s, with the impetus to reduce engine emissions, major automotive engine manufacturers turned to even lighter weight alloys such as magnesium to reduce engine weight, thereby reducing automobile weight, reducing power requirements, and reducing emissions. Magnesium alloys are approximately 33% less dense than aluminum and 75% less dense than cast iron. Therefore, when designing a new engine for mobile electric power generation, from a weight optimization perspective, magnesium alloys are considered the most desirable, aluminum alloys the second most desirable, and cast iron the least desirable. Of the magnesium alloys, magnesium-aluminum (AM) and magnesium-aluminum-zinc (AZ) alloys have excellent room temperature strength and/or ductility but do not exhibit good creep resistance. AZ alloys have good corrosion resistance properties as well. Magnesium-aluminum-rare earth (AE) and magnesium-aluminum-silicon (AS) have been developed to improve elevated-temperature performance. AS alloys only provide a marginal improvement in creep resistance. AE alloys are expensive due to rare-earth additions, have poor die cast properties, have high oxidation rate, and low fatigue resistance. Industry has devoted significant investments of time and money to develop new high temperature magnesium alloys. An alternative solution is to design the engine with reduced stress, temperature, and creep requirements that do not exceed the material properties of currently available materials.
As previously discussed, the second potential area for significantly reducing the weight of a portable generator is the alternator. The greatest potential for weight savings is to design the alternator as an integral component of the engine. That is, design the generator as an integrated unit, not the coupling of individual units. Fully integrated systems where the alternator is integral to the engine flywheel are common in the marine industry. However, the electric power generated by the alternator is small compared to the mechanical power generated by the shaft. The mechanical power is typically used to drive a mechanical mechanism such as a propeller and the electrical power is typically used for auxiliary lighting and control equipment. Those alternators are not designed to utilize all of the mechanical power generated by the engine shaft. In generators, where a much higher percentage of the mechanical power is converted to electrical power, there is a larger portion of waste heat that is developed due to the conversion. The waste heat is produced due to the inefficiency of the power conversion devices and must be removed for proper operation of the generator. Further, marine engines with flywheel alternators are typically water-cooled.
In portable electric generators, a fan sufficient for removing large quantities of waste heat produced by power electronics must be incorporated. Finned structures common on existing flywheel/alternators are not able to provide ample cooling to both the engine and the alternator. Most often the fins merely ventilate low power electronics used to create a spark for spark ignition type engines or low power electronics used to run auxiliary systems. Larger power generation creates larger quantities of waste heat that can not be removed by simple paddle style circulators.